The present invention relates generally to an extracorporeal blood processing system and more particularly to a method and apparatus using a removably coupled force sensor capable of indicating pressure in a blood removal conduit and/or a blood return conduit.
Extracorporeal blood processing systems remove blood from a patient""s body, process the blood for some purpose and return it to the body. One type of extracorporeal blood processing is an apheresis procedure in which blood from a donor is directed to a blood component separation device (e.g., centrifuge). The blood is separated into various blood component types (e.g., red blood cells, white blood cells, platelets, plasma) for collection or therapeutic purposes while the remainder are returned to the donor. Apheresis procedures are often conducted at clinics with multiple donors being processed on a single apheresis machine in a single day. Another type of extracorporeal blood processing is an oxygenation procedure in which blood is removed from a patient, directed to a blood oxygenation device where the blood is oxygenated and returned to the patient. This blood procedure is useful in ensuring that freshly oxygenated blood is circulated to the patient during surgery when the heart and lungs are stopped. Other extracorporeal blood processing techniques, such as hemodialysis, blood salvage and blood washing are also well-known.
In extracorporeal systems, such as those mentioned above, positive and negative pressures must be accurately monitored as blood is removed from and returned to the patient. In addition, it is highly desirable for blood processing systems to use a disposable assembly for any portion of the system which contacts the blood. For such systems, the mechanism for monitoring pressure must be capable of connecting with and monitoring blood pressure in the disposable assembly.
In previous blood processing systems, pressure has been measured using a pressure sensor in communication with a blood conduit. In one such embodiment, a diaphragm is incorporated into the blood conduit, and blood, in the conduit, contacts one surface of the diaphragm while a captive air space is in contact with a second surface of the diaphragm. A pressure sensor communicates with the captive air space. In addition, the pressure sensor measures the pressure changes in the captive air space as the diaphragm flexes in response to the pressure changes in the blood conduit. Such a system is not entirely satisfactory. If an air leak develops in the captive air space, the sensor is not capable of accurately measuring pressure in the blood conduit. In another blood processing system, pressure in a blood conduit has been measured by a force sensor placed around the blood conduit. To determine the pressure of the blood within the conduit, the force sensor measures the expansion of the blood conduit. These pressure monitoring systems have been known to produce less than accurate pressure measurements, especially for negative pressures.
A need, therefore, exists for a blood processing system having a sensor that is capable of measuring positive and negative pressure of a fluid flowing through a conduit. Such a system should be suitable for use in measuring pressures within a disposable assembly, and the sensor should be capable of being removably coupled with the disposable assembly. Moreover, such a system should avoid the durability problems associated with pressure measuring systems using captive air spaces.
The present invention generally relates to extracorporeal blood processing systems. Each of the various aspects of the present invention may be incorporated into, for example, an apheresis system (e.g., where blood components are separated) and other extracorporeal blood processing applications which are within the scope of the present invention.
An extracorporeal blood processing system which embodies one or more aspects of the present invention generally includes a blood removal conduit for transporting blood from a donor/patient and a blood return conduit for transferring blood to the donor/patient. A portion of the blood removal conduit and a portion of the blood return conduit are in fluid communication. A disposable assembly is provided that has a plurality of integral passageways used to transport blood. Each of the passageways is partially defined by either the blood removal conduit or the blood return conduit. In one embodiment, the disposable assembly comprises a molded cassette member that has a series of integral passageways which partially define the blood removal conduit and the blood return conduit.
In another aspect of the present invention, a pressure sensing station is connected in direct fluid communication with either a portion of the blood removal conduit or a portion of the blood return conduit. The pressure sensing station includes a diaphragm having a first surface in fluid communication with either the blood removal or blood return conduit. A second surface of the diaphragm is removably attached to a sensor. The diaphragm may comprise a flexible elastomeric material.
In one aspect of this embodiment, the sensor includes a pressure measuring mechanism, such as a strain gauge. Through the pressure measuring mechanism, the force exerted on the first surface of the diaphragm can be measured. The resultant force exerted on the diaphragm corresponds to the pressure of the blood in the corresponding blood conduit. In yet another aspect of this embodiment, the sensor may be a piezoelectric distance sensor for measuring the distance the diaphragm deflects and converting this distance into a pressure in the blood conduit.
In yet another aspect of this embodiment, a ferromagnetic material is attached to the second surface of the diaphragm, and a magnet is attached to the sensor. The magnet is capable of being directly coupled to the ferromagnetic material on the second surface of the diaphragm. As such, this coupling of the ferromagnetic material and the magnet create a removable attachment of the diaphragm and the sensor. In an alternative aspect, the magnet may be attached to the diaphragm and the ferromagnetic material may be attached to the sensor.
In a further embodiment of the present invention, the extracorporeal blood processing system can include a disposable assembly as broadly discussed above. In addition, the extracorporeal blood processing system includes a sensor which measures a quantity corresponding to positive and negative fluid pressures and which can be removably attached to the second surface of the diaphragm of the disposable assembly. The sensor may be removably attached to the second surface of the diaphragm.
In one aspect of this embodiment, a probe having a vacuum chamber is provided for interfacing with the second surface of the diaphragm. The probe is connected to the sensor, and when a vacuum is created in the vacuum chamber the probe is coupled to the second surface of the diaphragm.
A means for detecting a state of coupling between the vacuum chamber and the second surface of the diaphragm, such as a means for monitoring air flow, may also be provided. When air flow is detected, the probe is not connected to the second surface of the diaphragm and vice versa.
In another aspect of this embodiment, the diaphragm includes an elongated member attached to and extending from the second surface of the diaphragm. A means for attaching the second surface to a sensor is provided. The means for attaching includes a means for capturing the elongated member. In this aspect, the elongated member may have a shaped end. The means for attaching may further comprise a receiving structure having a complementary shaped opening corresponding to the shaped end of the elongated member. In addition, the means for attaching may also include a receiving element having an opening wherein the opening has a first size for accepting the shaped end and a second size, smaller that the first size, for capturing the shaped end.
In even another embodiment of the present invention, a method for measuring pressure in an extracorporeal blood processing system is provided. This method includes introducing blood from a donor/patient into a disposable assembly, wherein the disposable assembly has at least one blood conduit with a diaphragm member disposed within a wall of the conduit. The method further includes determining a pressure in the at least one blood conduit. The step of determining may include measuring a force of the blood on the diaphragm using a force sensor or displacement of the diaphragm. The measured force or displacement may then used to calculate a pressure of the blood in the blood conduit. The disposable assembly and extracorporeal blood processing system as broadly described above are useful in the method of the present invention.